In current medical practice, in order to obtain real-time visualization of the vascular system of a patient, a fluoroscope may be used. The fluoroscope is an X-ray machine which can image moving (or non-moving) internal anatomy. The most common type of fluoroscope found in a vascular surgical suite is the “C-arm” fluoroscope. In the C-arm fluoroscope, the X-ray source and the X-Ray detector are connected together by a “C”-shaped gantry that can rotate (with two degrees of freedom) around the patient's body. See, for example, FIG. 1.
Because the imaging energy used in a fluoroscope comes from an X-ray tube, the anatomy that is X-ray opaque (e.g., bone) is highly visible, while tissue that is X-ray transparent (e.g., soft tissue, such as blood vessels) is substantially invisible. As a result, a contrast agent (e.g., iodine-based) is typically used to enhance the visibility of the lumen of the blood vessel. In this respect it will be appreciated that the contrast agent must be administered in sufficient quantity, and at the right time relative to the moment of X-ray capture, in order to produce good images.
Through the use of a C-arm fluoroscope and such contrast agents, a surgeon can see enough of a patient's vascular anatomy to perform procedures such as the endoluminal repair of an abdominal aortic aneurysm (AAA). Such endoluminal repairs are typically performed using a stent graft which is advanced to the surgical site through a catheter. The catheter is commonly inserted into the femoral artery and then advanced up the femoral artery, through the iliac branch and along the aorta to the site of the aneurysm.
During the endoluminal repair procedure, the stent graft must be carefully positioned within the aorta so as to avoid blocking the renal arteries. In most modern fluoroscope systems, the renal arteries can be seen with a “road map” view, in which the blood vessels are enhanced so as to appear white, and the bones of the spine are digitally removed, i.e., through a subtraction process, so as to render the view more clearly.
To produce the road map view, the spinal bones are first imaged using fluoroscopy so as to produce a “mask” image. In this mask image, the bones appear dark and the blood vessels are effectively invisible (because no contrast agent is used). Then, a fluoroscopic image is taken using a contrast agent so that both the blood vessels and spinal bones are dark. The mask image is then “subtracted” from the contrast image so as to produce a resulting image which includes only the dark, contrast-enhanced regions of the blood vessels. The pixel values in this resulting image are then digitally inverted, so that the dark blood vessels become white, whereby to produce the final image shown in FIG. 2.
While effective, the foregoing process requires the generation of multiple images, the use of a contrast agent which may be deleterious to the patient's health, the processing associated with image subtraction, etc.
Thus, it would be desirable to provide a new visualization process which does not require the use of the contrast agent, among other things.